secretary of state hillary clinton. u.s. hopes diplomacy can stop iran. netanyahu argued ultimatums don't lead to war, they prevent them. >> i believe faced with a clear red line iran will back down and this will give more time for sanctions and diplomacy to convince iran to dismantle its nuclear weapons program altogether. >> david martin has more on netanyahu's plea for action. >> reporter: it looked like a cartoon but it was deadly serious. israel's prime minister netanyahu drew the red line that would trigger an attack on iran's nuclear program as clearly as it has ever been drawn. >> a red line should be drawn right here. before -- before iran completes the second stage of nuclear enrichment necessary to make a bomb. >> reporter: that second stage is taking place at this underground facility near the holy city of qom where iran is enriching uranium to a 20% level of purity, one step away from the 90% needed to build a bomb. according to the latest report by u.n. inspectors, iran has about 200 pounds of 20% uranium. roughly two-thirds of what it would